Cadmium plating



4 LOUTH and ('2) AIiTHUR WHITE YOUNG,

Patented May 5, 1925.

UNITED STAT-ES PATENT OF 1,537,041 FICE.

niAonIcE E. LOUTH AND ARTHUR wrirrn YOUNG, or xoxomo, INDIANA, ASSIGNOR-S TO UDYLI' IE BROGESS COMPANY,- OF KOKOMO, INDIANA, A CORPORATION OF IN- DIANA.

No Drawing. Application filed June 5,

To all whom it may concern: Be it known. that we, (1) MAURICE E.

citizens of the United States, residing at Kokomo, in the county of Howard and State of Indiana, haveinvented certain'new and useful Improvements in Cadmium Plating, of which the following is a specification.

We have found in electroplating with cad mium that it is possible to vary and coordinate the ..'various factors involved, to wit, the composition of the bat-h,-the.type of anode, the ratio of active toinactive anode surface, the ratio of anode to cathode surface, the use of brightening or. addition agents, and the current'density in such a .way as toproduce a number of desirable re-- sults, among which may be mentioned the maintenance'of the electrolytic. bath at maximum efiiciency over a long period of time I and the productionflof coatings having the I so ' stance by dissolving cadmium oxide or hy- Gil ' desired characteristics.

The most important factor in the present invention is the bath composition. In

referring to bath compositiom-we do not mean to indicate-the kind of chemical sub stances inyolved'but rather the relation of the chemical substances in the bath to each other. We employ a sodium cadmium. cyanide bath which may be prepared, for indrate or carbonate in an aqueous solution of sodium' cyanide. The resulting bath contains (-1) sodium cadmium cyanide, (2) sodium hydroxide in case "cadmium oxide or hydrate is used in preparing the bath or sodium carbonate in case cadmium carbonate is used 1n preparing the bath, and (3) sodium cyanide used in excess of-that required to convertjthe cadmium oxide, hydrate or carbonate to sodium cadmium cyanide. .The

.composition of the sodium'cadmium cyas -nide bath may vary rather widely; For example, it. may contain from to 6 ounces of cadmium per gallonand from'2 to 6 ounces of free sodium cyanide: per callon;

B free sodium cyanide is meantt 1e sodium cyanide used in makingup the bath in excess of that which is use in'conv'erting' the cadmium oxide, hydrate. (gr-carbonate" dissolved therein to sodiumcadmium cyan-.

.to cause undesirable I .deposlts; *Lead 1n ounce per gallon, ounces per. gallon per gallon.

GADMIUM PLATING.

1924. Serial o. 718,155.

ical standpoint. The sodium hydroxide or carbonate content of the bath resulting from the interaction of the sodium cyanide with the cadmium oxide, hydrate or carbonate of course, unless extra sodium carbonate or l1'y-- cut effect it is undesirable from an economdroxide is added, will be chemically equivalent to the quantity of cadmium oxide, hydrate or carbonate dissolved, and although we donot regard the addition ;of' extra sodium carbonate or hydroxide to the bath as being advisable, such additions are not to be regarded as a departure from our invenion.

-A bath suitable for commercial use may be prepared as follows: To a Water solution of -sodlum cyanide containing about. 8% ounces of sodium cyanide per gallon there is added about 2 ouncesof cadmium oxide completely, giving a solution containing about 5 ounces'of free sodium cyanide and about 2 ounces of cadmium per gallon.

The cadmium oxide dissolves As is-indicated above, the limits stated I for the free sodium cyanide content of the bath are not merely arbitrary limits but have a definite relation to the results tobe produced. In. the same way the range of cadmium content of the baths'pccified bears a definite relation to the results to be produced. At below gallon of electrolyte the bath is difficult to, maintain, while atabove 6 ounces per gallon there is a tendency, when electroplating at average current density to be described here- 'nafter, 'for the electrodeposit to tree.- A cadmium content of about 2 ounces per gallon therefore is preferred, since we have -:found' in practice. that this content gives good coatings and 1s easily maintained and the tendency to deviate from this content f beyond either limit is the minimum.

I The cadmium oxide, hydroxide or carbonateusedin making up the bath should be pure and particularly with reference tothallium, tin and lead which we have found quantitiesas small as 0.1% of the cadmium causes serious trouble.

4 ounce of cadmium per The anodes to be used with the above de 10 scribed sodium cadmium cyanide bath may be wholly inactive, for instance, all steel, or

wholly active, that is, pure cadmium, or a rent density and anode to cathode ratio tosteel .or carbon may be used. The use of ,crease in the cyanide content .of t he whichrequires occaslonal addit ons of combination of active and inactive material, for anstance a combination of steel and metalhc cadmium 1n a definite ratio to each other, which ratio bears adefinite relation to the bath composition, as will appear herein after. 4

' With a sodium cadmium cyanide bath as described above and within the limits'of curbe described hereinafter, there may be used either all cadmium anodes, or all inactive anodes such as steel or anodes made up of both cadmium and steel or other inactive material in varying proportions. At the lower limit of free sodium cyanide content, that is at ounce per gallon and up to-'2 ounces per gallon, inactive anodes such as inactive anodes,however, is,not preferred, because it requires for :the' maintenance of the bath suitable additions of cadmium, and besides, particularly when graphite anodes are used it appears that the cyanide radicalfree sodium cyanide content of the bath must be maintained'at-or abo 'e ounces per gallon, otherwise polarlzation takes .place with a correspondingdiminution-in plating values. At above 2% ounces of free sodium cyanide per gallon with pure cad mium' anodes the cadmium content of the bath tends to increase. The use of pure .cadmium anodes is not preferred, because it is difiicult and troublesome to maintain the free sodiumc anide content-of thebath at such a figure,'a out 2 ounces per gallon, that neither polarization ortoo great a building up of the cadmium content of the bath' Wlll 0601112; We therefore; preferthe use of combined soluble and insoluble anodes, the active and inactive surface of which may be variedin a bath containing 2% ounces or more of freesodium cyanide per gallon. The ratio of active to inactive surface in the combination. solubleand insoluble anodes varies widely, depending Y upon the composition of the bath and other specific setof conditions. -The preferred ratio must be determinedbyexperiment in p each partlcular case. The following specific factors within the limits heretofore defined. It is impossible to-state a general rule for thedetermination of the best ratio 'of active to inactive anode surface'under all-or any example is illustrative:

In a 500 gallon plating bath in continuous operation containing on an average about 2 ounces of cadmium and about 5 ounces of freesodium cyanide pergallon, in the use of which a cathode surface-to anode surface ratio of from 1%1 to 11.was maintained, an active to inactive anode surface ratio of to gave satisfactory results. In the use of this bath the cadmium content of the bath was found to vary within 4 ounce per gallon above and below the average cadmium contentand the losses of sodium cyanide v were very small, a few pounds per month. In general it may be stated that the active to inactive anode surface ratio may vary from about 1-3 to about 3-1.

. The current density which may beused along with the other factors, and particularly with reference to the bath composition defined, may vary from 4 to 100 amperes per square foot. 'However, whena brightening agent is used as described'below, the upper limit of current density is about 30 amperes per square foot, above which limit the coat- .lngs become less' lustrous and more gray as the current density increases. p

The plating may be carried out either in the presence or absence of addition or.

brightening agents, but theuse of addition agents is preferred. If addition. agents are 3 not used the coatings may be either dullvwhite, silver white'or gray, depending upon the'current density. Such coatings are soft and are apt to be cut'through by bufiing, but they are satisfactoryfor some classes of rough work such as castings. The? use of addition agents is practically indispensable for various classes of work such as that upon which a high polish is desired, or which-is to be color-buffed or over-coated with nickel. By the use of addition agents the coatings are made physically harder and denser and given a bright lustrous sheen. Such coat-.

ings produced with the useofaddition agents in many cases have. sufficient luster so that the use of other finishes is unnecessary. They may be buiiedwithout cutting through and are more resistant toblows andscratches and more continuous-when tested ;for pin holes than coatings madewithout the use of addition agents.

Various addition agents mayflbe used, but

we prefer the use of. milk or protein additlon agents, such as. wool and casein. Of

Wool from to 1'O'grams per gallon of electrolytic bath may -be-used,' about 1% grams being the-usual average. YThe wool may beadded-to the plating bath by dis- 1 :solvingit in concentrated Warm caustic soda solution. and adding this solution to the bath. Casein may be used in quantities varying from to 2 /2 gramsper gallon. Casein is added in the form of a solution in Warm dilute aqua ammonia. Milk is the preferredaddition agent and is used prefer:

ably in the 'formof these-called evaporated. milk which is an unsweetened product made .by evaporating whole milk under vacuum to about one-half its original. volume. Evapo-, rated milk may be. used in quantities vary-- ing from to 40 cc. per gallon, a satisfac I 'tory' average amountbeing 10 cc. per gallon.

'inthis connection that we do not ur invention therefore involves gener-' ally the determinationand coordination of the various factors involved in electroplating cadmium from cyanide solutions and .more

.particularlythe determination ofthe relations of the various factors. involved such as bath .composition,- active to inactive anode surface ratio, anode tocathode ratio, cur-.

rent density, etc., to each other. Itis noted a m be the first to propose the electroplating of cadmium from cyanide solutions, or the use of wholly active or wholly inactive or combined active and inactlve anodes or the use a Y of brightening agents in general or the particular bri htening-agents referred-to in the electroplatlng ofcadmium... It 'was, of

course,-also known prior to our invention to vary the. composition of the bath the anode to cathode ratio, the current densityetc.

Our invention lies in the coordination of these various factors in 'sucha wa that sufrom a sodium cadmium cyanide bath conabout 5 taining from to ,6 ounces of cadmium and from 2 to 6 ounc es of free sodium cyanide per gallon of bath.

v 3. Processof.electroplating'with cadmium which comprises elect-ro-depositmg cadmium from a sodium cadmium cyanide -bath'containing about 2 ounces of cadm um and gallon.

4.; Process of electroplating with cadmium which comprises electro-depositing cadmium from a sodium cadmiumcyanide bath containing from to'@6 oun taining'from to 6 ounces of cadmium and at least 2 ouncesof free sodium cyanide per gallon in-thepres'ence of an anodecomprising metallic cadmium. 5. Process of electroplating with cadmium which comprises electro-depositing cadmium of cadmiu from a sodiunrcadmiumicyan' ounces of free sodium cyanide per from 2 to '6 ounces of free sodium cyanide per gallon of bath in the presence of an anode comprising active and inactive material, the ratio of the surfaces of which lies between'the-limits 1 to 3 and 3 to 1.

' 6. Process of electroplating with cadmium which comprises elect-ro-depositing cadmium from a sodium cadmium cyanide bath con-' taining about 2' ounces of cadmium and about 5 ounces of'free sodium cyanide per gallonin the presence of an anode comprising active and inactive surfaces, the ratio of which is about to 55. 7. Process of electroplating with cadmium which comprises:electro-depositing' cadmium y 'from a sodiumcadmrum cyan de bath containing from to 6. ounces of cadmium and to 10 ouncesof free sodium cyanide per gallon at a current density of from 4 to '100amperes persquare foot. y

8. Process of electroplating with cadmium which comprises electro-depositing cadmium Y.

.froma sodium cadmium cyanide bath at a current density cream-.4 to 30 amperes persquare foot inthe presence of an addition age'nt.;-.;

' '9. Process of electroplating withcadmium v which comprises electron-depositing cadmium from a sodium cadmium cyanide; solution containlng from A to 6 ounces of cadmium and from 2 ,5 to 6 ounces of free sodiumcy- 'anide per gallon in thepres'ence of an anode comprising metallic cadmium-and an. inact1ve conductive-material at a current density of from 4 to amperesper square-foot.-

10. Process of electroplating with cadmium whichv comprises electro-depositing cadiniumfrom a sodium cadmium cyanide solu-v tion containingfrom A to 6 ounces of cadmium and from 2 to 6 ounces of freesodiumcyanideper gallonfin the presence of an--- anodecomprising metallic cadmium'and an inactive conductive material at a current density of. from [to 30 amperes per square ;11; Process of electroplating with cadmium which comprises electro-depositing cadm-ium from' a sodium cadmium cyanide bath containing about 2 ounces ofcadmium i and 5 ounces of free sodium-cyanide, using 'a combined cadmium and-steel anode theratio of; cadmium to steel surface of said anode being about 45- to.'5 5'and the ratio of;

cathode'su'rface to'anode surface being from 1 +1 to 1-1, at a currentdensity' of from 4 to 30 amperes. per square foot-in ence of an addition agent.

tures.

the presv In testimony'w'hereof, we aifixour signa- 1 05 'ffOOll in the, presence of janaddition -agent. v w 

